A comprehensive series of mechanical properties tests will be performed during this three-year effort, the principal component of which is a study of fatigue life of elastomers in whole human blood, as part of the Biomaterials Program of the Devices and Technology Branch of NHLBI. The fatigue life of the elastomers will be evaluated by three approaches: uniaxial tensile fatigue, flex, and cut or crack growth tests; biaxial tensile fatigue, with similar and different strains in the major axes; and fatigue testing of an end-use component configuration such as will be used on heart assist blood pumps.